Reclosers and circuit breakers are electromechanical switches that open and close one or more phases of an electrical power line, such as in response to an overcurrent in the power line. The term “recloser” in this application may include various fault interrupting devices, such as reclosers, reclosing circuit breakers and the like.
In general, when an overcurrent of sufficient magnitude and duration flows through a recloser, a tripping action is initiated, circuit interrupting contacts open, and an operation counter advances one count. After a pre-set time delay, the circuit interrupting contacts may be automatically reclosed, thereby re-energizing the line. If the fault was temporary, such as due to a tree branch or animal momentarily contacting the line, and the fault was cleared before the recloser was reclosed, the recloser will remain closed and reset to its original condition after a short time delay such that the recloser is ready for the next operation. If the fault was not cleared before the recloser was reclosed the first time, the tripping action is again initiated to open the circuit interrupting contacts. The recloser will automatically reclose the contacts after a further, and typically longer, time delay.
However, not all faults that occur on electrical power lines are temporary. Rather, some faults are of a more persistent or permanent nature, such as where a storm causes an entire pole structure to fall to the ground. In response to a permanent fault, the tripping and reclosing sequence will repeat a predetermined number of times, as counted by the operation counter, until a lockout function is initiated to lock the circuit interrupting contacts open and prevent further reclosings into a permanent fault. Thus the recloser will have reclosed into a permanent fault, and passed the available fault current into the circuit, several times before completing the entire reclosing cycle and locking-out to prevent further reclosing of the circuit interrupting contacts.
When faults are temporary, auto-reclosing in most cases is advantageous and improves the service reliability. The current practice for majority of utilities upon discovering a unit that is locked out, i.e. open with automatic operation disabled, is to immediately try to reclose the unit to re-energize the line without performing any inspections or checking to determine the fault status. A unit may lock out erroneously or in the presence of a permanent fault. Multiple re-closings are performed until the unit successfully closes or locks out after a predetermined number of reclosing attempts. The practice of conventional auto-reclosing is detrimental to system components and system reliability and power quality. Especially, auto-reclosing on a faulted line leads to accelerated failures and power quality problems.
US2013218359 A1 discloses a system configured to analyse and/or respond to faults detected during the operation of a power transmission system. The system analyses operational data such as circuit breaker status, voltage values, current values, waveforms, etc. obtained from components of the power system to develop and process a pattern of the fault phase voltage. Based upon the analysis of this faulty phase voltage pattern, the system determines if a fault is transient or permanent.